The invention pertains to a versatile stereotactic device useful in a number of methods, including numerous modes of medical imaging. More particularly, the device and methods of the present invention relate to a non-invasive stereotactic method of reproducibly imaging portions of a patient""s body, such as the patient""s head and portions of the patient""s spine in the proximity of the head. Thus, imaging modalities, including magnetic resonance (MR) imaging, magnetic resonance spectroscopy, computer-aided tomography (CT), positron emission tomography (PET), single photon emission computed tomography (SPECT), electroencephalography (EEG) or magnetoencephalography (MEG) and the like can be used to monitor, diagnose, or detect pathologic conditions and to follow their development, progress, arrest, or remission. The device and methods of the invention are especially applicable to permitting more routine head examinations, pre-surgical planning and providing post-surgical evaluations and prognoses.
In head examinations involving magnetic resonance imaging, computer-aided tomography and other such techniques, it is desirable to have a well-defined, reproducible coordinate system to record and/or compare the locations and sizes of lesions, tumors and other structures of interest. Though there are a number of known devices and techniques for potential application to these types of examinations, these known devices and techniques are generally not suitable for xe2x80x9croutinexe2x80x9d office examinations, in which factors such as ease of use, speed of use, comfort, cost, accuracy and reproducibility are of major consideration. Indeed, existing devices are often heavy, unwieldy, cumbersome and require that the devices be affixed to the subject using pins, screws, bolts, brackets, staples and the like.
Several methods have been proposed to find the relative position of a scan xe2x80x9cslicexe2x80x9d by using anatomical landmarks. In these methods, the size and position of predetermined anatomical structures, such as the lateral end of the internal auditory canal, are used as reference points to help locate and compare lesions and other features of interest. See, e.g., Tan, K. K. et al., in J. Neurosurg. (1993) 79:296-303. A problem with this technique, however, is that the image resolution in the scan slice direction (i.e., the z-direction) is poor compared with the resolution in the scan in-plane (x-y direction). Because of this poor resolution, it is difficult to make precise positional determinations. Moreover, these methods also require a degree of anatomical knowledge which may strain the capabilities of the average MR technologist.
As an alternative, the art has developed devices, such as frames and xe2x80x9chalos,xe2x80x9d to facilitate positioning for stereotactic surgery. These devices are rigidly affixed to the patient being imaged and to an imager platform and provide reference points or lines to facilitate the determination of the orientation of the patient""s head. See, e.g., U.S. Pat. No. 4,341,220, which discloses a stereotactic surgical frame with fiducial plates that surround the patient""s head in the fashion of a boxer""s headgear and which provides several non-collinear fiducial points in cross-sectional scans. Most stereotactic frames are fixed to the patient""s skull directly, usually by bolts or screws, as noted previously. Clearly such methods are not suitable for xe2x80x9croutinexe2x80x9d office examinations.
So-called non-invasive, stereotactic devices have also been described. The Gill-Thomas stereotactic frame, which is based on the Brown-Roberts-Wells neurosurgical frame, was designed to be used for a series of stereotactic radiotherapeutic operations. See, Graham et al., in Radiotherapy and Oncology, (1991) 21:60-62. This device requires that it be affixed to the patient by a block, tailored for individual patients.
Another device, designed by Laitinen et al., is fixed to the patient by means of a nasion support and two ear plugs. See, e.g., Laitinen et al., in Surg. Neurol. (1985) 23:559-566 and U.S. Pat. No. 4,617,925. However, this device is then affixed to the imaging couch or table. Hence, this device is able to permit reproducible scans only by relying on the fixed position of the patient against the couch or table with respect to the machine coordinate system. Again, affixing the patient to the machine may makes the patient uncomfortable during the scan. See, also, U.S. Pat. No. 5,330,485, disclosing a cerebral instrument guide frame that rests on the bridge of the nose (i.e., about the nasion) and which contains plugs for insertion into the external ear canals.
Stereotactic devices are typically fashioned from precision aluminum alloy and are very expensive for all except non-routine use. Moreover, it is usually cumbersome and time consuming to affix these devices to the patient, adding to their unsuitability for routine examinations.
The state of the art suggests that stereotactic devices be equipped with radiographic markers that are visible in scans of a patient""s head. For example, U.S. Pat. No. 4,923,459 discloses a stereotactic frame that also includes radio-opaque rods arranged in the configuration of the letter xe2x80x9cNxe2x80x9d to facilitate localization of a surgical target. U.S. Pat. No. 4,608,977 discloses a helmet-like, stereotactic frame that includes such N-shaped xe2x80x9clocalizingxe2x80x9d rod to facilitate the determination of the location of a CT scan cross-section. Likewise, U.S. Pat. No. 4,638,798 discloses a halo-like stereotactic frame that has a ring with a plurality of pins of differing lengths extending therefrom. The relative location of a scan can be determined from the relative location of the ends of the pins.
Though such devices can be used to determine the location of a head in x-y space, and to determine the relative location of each imaging xe2x80x9cslice,xe2x80x9d they do not permit the position of a head to be fully determined, e.g., as where the head is tilted in the imaging plane.
In addition to the limitations described above, the prior techniques are not generally suitable for direct alignment of images obtained from different imaging modalities. That is, to permit the direct comparison of images obtained from different imaging modalities, say MR and CT, the patient must be re-aligned precisely with respect to the two machine coordinate systems. Alternatively, a correction can be made using image processing techniques after a second or subsequent scan has been taken. However, image processing has the drawback in that the resolution of the processed image is dependent on the quality of the scan data set. It would be desirable to alter a scan in real time such that scans from different modalities can be compared directly without the need for image processing.
In each of the known devices and methods, the anatomical coordinates of the patient are fixed in relation to a reference coordinate system, that is the machine""s coordinate system. Thereafter, the machine""s coordinate system is used as the reference coordinate system for each subsequent scan. Because of the difficulty in reproducing the machine coordinate system or because different machines are invariably associated with different, incompatible machine coordinate systems, it has not before been possible to relate directly scans from different imaging modalities. Moreover, it is not always possible to align directly scans from the same imaging modality (e.g., MR imagers) when comparing images obtained from machines made by different manufacturers.
It would thus be desirable to have a device and method whereby the reference coordinate system is independent of the machine or imaging modality. It would be desirable, moreover, to use a reference coordinate system xe2x80x9cpersonalxe2x80x9d to the patient as the reference coordinate system and, where possible, have the machine""s coordinate system fixed or adjusted relative to that of the patient to provide for scans that are reproducible, compatible and superimposable in the same or different imaging modalities. A system that enables the taking of imaging scans under such a patient reference or xe2x80x9cpersonalxe2x80x9d coordinate system would be of great utility and would be deemed a significant advancement in the art.
In view of the foregoing, it is an object of the invention to provide improved devices and methods of non-invasive, repetitive, radiographic examination of a subject, particularly of the subject""s head.
A further object of the invention is to provide such devices and methods that are readily amenable for use in xe2x80x9croutinexe2x80x9d examinations, as well as for surgical planning and follow-up.
A still further object of the invention seeks to provide improved devices and methods of stereotaxis (both invasive and non-invasive), which are low-cost, easy to use, comfortable and which provide accurate and reproducible results.
Yet another object of the invention relates to improving methods and apparatuses that can determine fully the position of a head and a scan plane, including when the head is tilted in the scan plane.
Other objects of the invention include providing a way or means for comparing directly scans taken by the same or different imaging modalities and providing a method for the reproducible placement of external markers, e.g., electrodes, on a patient.
The invention thus provides devices and methods for the non-invasive, imaging or radiographic examination of a subject. By xe2x80x9cimagingxe2x80x9d is meant any scanning or spectroscopic technique that provides information that can be recorded on a tangible medium (e.g., photographic film, slides and the like) or electronically for storage, later retrieval, or manipulation. Moreover, the scanning or spectroscopic technique may also give rise to an image that is viewable, e.g., on a screen or monitor. The immediate objective, of course, is to provide information regarding, or an image of, the internal organs or tissues of a subject. Such scanning or spectroscopic technique or imager can use a wide variety of electromagnetic radiation (or for that matter any suitable source of energy) to probe or excite internal atoms, ions, molecules, structures, cells, tissues, or organs, including but not limited to radio waves, infrared, ultrasound, ultraviolet, X-rays, electron beam, alpha-, beta-, or gamma-rays or particle emissions.
Accordingly, the invention provides a stereotactic device that is intended for use with an imager and generally comprises a frame equipped with localizing means and affixing means. The localizing means comprises one or more localizing arrays that provide one or more imager detectable signals, while the affixing means comprises non-invasive fittings for placement about the periphery of the subject and which permit the reproducible positioning of the frame on the subject. From the signals is derived a personal coordinate system that serves as a reference coordinate system for imaging scans taken of a subject on which the frame is positioned. This personal coordinate system is independent of any machine coordinate system. (Contrast the device of Laitinen et al., for example, which must be attached to the imaging table or couch to xe2x80x9cfixxe2x80x9d the device""s (and consequently the patient""s) coordinate system to that of the machine coordinate system.) In a specific embodiment of the invention, the localizing means comprises localizing arrays or individual reference elements. Alternatively, the localizing array may be made up of one or more reference elements. The resulting three-dimensional reference coordinate system is specific or xe2x80x9cpersonalxe2x80x9d to the subject and is independent of the machine coordinate system.
The device, as described further below, may be reproducibly positioned to the subject without the need for an invasive affixing means, such as staples, pins and/or bolts (i.e., the device of the invention is xe2x80x9cnon-invasivexe2x80x9d; non-invasive can also mean the absence of a surgical intervention or of a breach of a subject""s body).
The invention also relates to method of obtaining imaging scans of a subject which includes providing a non-invasive stereotactic device that is positioned reproducibly on a subject and which device establishes a personal coordinate system (PCS) associated with the subject. Again, the PCS is independent of a machine coordinate system (MCS) associated with an imager.
Subsequently, using an imager having an MCS, an imaging scan of the subject is taken (including the stereotactic device) to establish the PCS of the subject. The MCS of the imager is then manipulated to bring the MCS in substantial alignment with the PCS of the subject. One or more additional imaging scans of the subject are taken next, with the MCS of the imager substantially aligned with the PCS of the subject, to provide a first set of imaging scans.
In yet another aspect of the invention, a method of obtaining imaging scans of a subject taken over different time periods is disclosed. The method comprises taking at a first time period, using an imager, a baseline imaging scan that is relatable to a personal coordinate system (PCS) and a first machine coordinate system (MCS). The PCS, by definition, can be regenerated from the subject in a substantially reproducible manner independent of the imager""s (or machine""s) coordinate system. At a different time period, using a second imager, at least one follow-up imaging scan is taken, which scan is relatable to the PCS and a second MCS. The second MCS is then manipulated, such that the relationship between the second MCS and the PCS is substantially the same as the relationship between the first MCS and the PCS. At least one additional follow-up imaging scan is then taken, which imaging scan can be superimposed on the baseline imaging scan. The second imager may be the same as or different from the initial xe2x80x9cbaselinexe2x80x9d imager. It should be understood that follow-up scans can be taken over a wide range of time periods, from very short, essentially back-to-back scans to much longer time periods of days, to weeks, to years.
A further method of the invention relates to yet another method of obtaining imaging scans of a subject. The method comprises providing a subject with a non-invasive stereotactic device that is positioned reproducibly on a subject. The stereotactic device, when positioned on the subject, establishes a personal coordinate system (PCS) associated with the subject which, as always, is independent of a machine coordinate system (MSC) associated with an imager. The method continues with a step of taking, using a first imager having a first MCS, at least one imaging scan of the subject including the stereotactic device to establish the PCS of the subject and to relate the PCS of the subject to the first MCS of the first imager. The next step involves taking, using a second imager having a second MCS, at least one imaging scan of the subject including the stereotactic device to reestablish the PCS of the subject and to relate the PCS of the subject to the second MCS of the second imager. The second MCS is then manipulated, such that the PCS is related to the second MCS in substantially the same way as the PCS is related to the first MCS. The method may further comprise taking one or more additional imaging scans of the subject with the second MCS of the second imager so manipulated.
In this manner, the invention provides a device and methods by which temporally different imaging scans from the same or different imaging modalities can be compared directly.
The device and methods of the invention thereby satisfy a long felt need in the art by providing a way to define or obtain a personal coordinate system that is independent of the machine coordinate system, the time at which the imaging scans are taken, the operator of the imager, the brand name of the imager, the model of the imager, or even the modality of the imager.
An exemplary stereotactic device and method of the present invention can thereby facilitate routine examinations of a patient or subject. In particular, the subject""s head can be easily and repeatedly examined with the confidence that imaging scans taken at different time periods can be superimposed or compared directly. In some cases, portions of the patient""s spine can also be viewed routinely, e.g., during regular, pre- and post-surgical planning examinations. The imaging modalities that can be used to advantage (or used with each other in any combination, except that the imaging modality that has a xe2x80x9cfixedxe2x80x9d xe2x80x94not adjustablexe2x80x94machine coordinate system should preferably be used to obtain the first, baseline, or initial set of imaging scans) include MR, CT, PET, SPECT, MEG, and other such imaging/radiologic scanning or spectroscopic techniques.
The invention relates to a method of using a radiographic device by establishing a personal coordinate system referenced to the body of a living organism, establishing a linkage between the personal coordinate system and a machine coordinate system of the radiographic device, and translating data captured in the machine coordinate system to data referenced in the personal coordinate system. A transformation matrix links the personal coordinate system and the machine coordinate system. The transformation matrix can be a rotation matrix or a matrix which combines rotation and translation. Alternatively, a rotation matrix can be combined with a translation vector to link the personal coordinate system and the machine coordinate system. The transformation matrix can be determined using data from a single slice of radiographic data or from data from two or more slices.
The invention is also directed to a system for reproducibly capturing radiographic images, including a radiographic scanner, a stereotactic device, and a computer controlling the radiographic scanner and receiving output information from the scanner to detect the location and orientation of the stereotactic device. The computer is configured to store data referenced to a coordinate system defined with reference to the location and orientation of the stereotactic device. The computer is configured to translate position information controlling the radiographic scanner into position information referenced to the coordinate system defined with reference to the location and orientation of the stereotactic device.
The invention is also directed to a system for reproducibly capturing radiographic images, including a network, a radiographic scanner, a stereotactic device, and a computer, connected to the network, controlling the radiographic scanner and receiving output information from the scanner to detect location and orientation of the stereotactic device. The network is connected to one or more of (a) a host computer, (b) a workstation and (c) a gateway.
The invention is also directed to a computer program product including a memory, and a computer program stored on the memory, the computer program containing instructions for a. establishing a personal coordinate system referenced to the body of a living organism, and b. establishing a linkage between the personal coordinate system and a machine coordinate system of a radiographic device. The computer program further contains instructions for translating data captured in the machine coordinate system to data referenced in the personal coordinate system.
The invention is also directed to a computer program product including a memory, and a computer program stored on the memory, the computer program containing instructions for determining location and orientation of a stereotactic device from either a single slice of radiographic data or from two or more slices.
The invention is also directed to a method of using a radiographic device, including fitting a stereotactic device to the body of a living organism so that the fitting is reproducible, and using the stereotactic device to determine the location of one or more data points from one or more radiographic scans of the body.
These and other aspects of the invention are evident from the discussion above and from the more detailed descriptions that follow of the preferred embodiments of the invention.